Even as Sweetgreen opened its 20th D.C.-area shop in the Navy Yard last week and signed a lease to launch a West Coast outlet in Los Angeles next year, the owners quietly unveiled a test kitchen at its Dupont store that will eventually have an impact on the eco-friendly salad chain's locations from coast to coast.

The Dupont outlet, the chain's second store originally opened in 2009, underwent renovations about six months ago, but the refurbishment was merely part of a larger goal: to prepare the shop for its role as a test kitchen, which was officially rolled out earlier this month to curious and (sometimes skeptical) customers.

As part of its new testing grounds, Sweetgreen has hired Michael Stebner, former executive chef for natural foods guru Andrew Weil's True Food Kitchen, to serve as culinary director for the chain. A large part of his job will be rolling out sort of experimental salads at the Dupont store to gauge customer feedback and sales, which will help decide whether the Sweetgreen owners should place them into the core rotation at its 26 other locations (and counting).

"We have been really focused, historically, more on the sourcing of the ingredients, the farmers," says Nic Jammet, one of Sweetgreen's three founders. "But now, going forward, we want to focus not just on the supply chain, but really on the innovation, the flavors and the menu and make sure that as we go to different cities, different regions, the menu can evolve and make sense where we are."

The Dupont store already offers a glimpse into the future of the chain. Just take a look at the menu above the counter, where there are 12 removable boards listing the salads available. Nine of them are "core" salads or, to be more accurate, wannabe core salads. Many are essentially auditioning for a place on the core menu all across the chain. The other three are seasonal bowls that will change five times a year, which is a significant shift from Sweetgreen's previous approach to its rotating salad options. The chain used to have a single bowl that would change once a month or 12 times a year.

The new approach is designed to treat the rotating salads as a seasonal section of the menu, a rather novel notion for a budding national chain. Sweetgreen is, then, treating its 27 stores as if they were chef-driven restaurants, changing the menu, more or less, with the seasons, with a bonus fifth makeover.

“Nobody’s really done what we’re trying to do: Scale seasonal fast healthy food that tastes good," says Jammet. “If someone comes in and it’s the first day of spring, they'll feel the difference here. People should feel that. The food should be different as the year changes.”

The seasonal salads will vary per store, depending on the ingredients available from farmers and distributors in the area, but the core salads will be tested and tracked at the Dupont location exclusively. When customers buy a test salad, they will be given a card that lists a Web address, where diners can then leave feedback on their leafy experiment. In other words, Washingtonians in general, and Dupont Circle residents in particular, will now be the arbiters, helping to establish what salads appear on the core menu at all Sweetgreen stores.

"I think Washingtonians have a very discerning palate," says Jammet. Plus, the Georgetown graduate adds, Washington "is where we’re from. This is where the concept was born. It makes sense for us to do it here."

Hummus Tahina, one of the new salads available for customers to evaluate at Sweetgreen in Dupont Circle. (Tim Carman/The Washington Post)

Among the salad experiments is the Hummus Tahina, in which red onions, grape tomatoes, baked falafel, yogurt, feta and a scoop of hummus sits atop organic mesclun and chopped romaine. Last week, I sat down with Jammet, Stebner and Casey Gleason, director of food and beverage for Sweetgreen. Jammet says the new creation "is actually a mixture of two salads that were on the core salad [menu]. One was kind of a Greek salad and one was kind of a Middle Eastern salad. So we decided to combine them."

"We've always wanted to find a place for hummus on our menu," Jammet adds.

Jammet is happy with the Hummus Tahina, which has already become popular among customers, he says. But the co-founder wants Stebner to re-engineer the spicy cashew dressing on the Rad Thai salad, in which citrus-marinated shrimp, carrots, cucumbers, spicy sunflower seeds and bean sprouts rest on mixed greens and cabbage.

"It's good," Jammet says, "but I still think the dressing needs to be a little more pronounced."

I ask Jammet what he means by "pronounced."

"You don't get much of the cashew flavor," he says.

The co-owner's opinion on the Rad Thai underscores the fragile nature of the salads at the Dupont Circle store: They may not stay long. Or they may be constantly tweaked until the culinary team is satisfied with the final product. "Nothing's safe on that board," Jammet says. "That's why we wanted to put this big plaque" out front, saying this "is not like a normal Sweetgreen."

Speaking of fragile, you'll notice one other major change at the Dupont store: no more fro-yo known as Sweetflow. The team decided to ditch the dessert as part of its streamlining process.

"As we kind of keep Sweetgreen moving in the right direction, we want to simplify and amplify," Jammet says, "and yogurt just doesn’t fit that.” As stores grow older, Jammet adds, and need to be renovated, Sweetgreen will likely drop yogurt from them, too.

The seasonal and test salads currently on the menu at the Sweetgreen at Dupont:

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